Reflex sympathetic dystrophy (RSD) is a pathogenic condition affecting a patient's extremities and characterized by persistent pain and swelling with vasomotor and sudomotor changes, and later atrophy. The precipitating cause of RSD is soft tissue injury. Fractures of the bones of the wrists are commonly associated with RSD. Chronic undiagnosed knee pain, with few clinical signs beyond hyperaesthesia and limited movement may suggest RSD. It may only manifest itself days, weeks, or even years after the soft tissue injury has been incurred.
Adopting clinical criteria, the following operational definition of RSD was adopted at the Sixth World congress of Pain:
"RSD is a descriptive term meaning a complex disorder or group of disorders that may develop as a consequence of trauma affecting the limbs, with or without an obvious nerve lesion. RSD may also develop after visceral diseases, and central nervous system lesions or, rarely, without an obvious antecedent event. It consists of pain and related sensory abnormalities in the motor system and changes in structure of both superficial and deep tissues ("trophic changes"). It is not necessary that all components are present. It is agreed that the name "reflex sympathetic dystrophy" is used in a descriptive sense and does not imply specific underlying mechanisms".
The pathogenesis and pathophysiology of reflex sympathetic dystrophy are most commonly characterized by impaired vasomotor control which usually results in vasodilation and increased skin temperature over the affected area, in the initial stages, and vasoconstriction and reduced skin temperature in the later stages. Also, the blood flow and skin temperature changes in the contralateral limb following cold stress of the affected limb are abnormal, thus suggesting a central nervous system abnormality.
There is currently no specific, accepted treatment for RSD, and cure of it cannot be assured. Vascular and perhaps neurological changes occur during the natural history of the disease. Some treatments are directed to those. For example, calcitonin, a vasoconstrictor, is often used during the early vasodilation stage, but is inappropriate at later stages when vasoconstriction predominates. In this stage, pharmacologic or surgical sympathectomy is effective in some cases. Immobilization of the affected limb is avoided, since this exacerbates the problem. Alternative therapies include corticosteroids, transcutaneous nerve stimulation, acupuncture and autogenic training.